In order to provide a homogeneous air/fuel mixture for a combustion chamber of gas turbines, an air/fuel mixture may be injected into a tubular swirling chamber of the turbine. When injecting a fluid, such as air, fuel or an air/fuel mixture, radially, a defined swirling of the air/fuel mixture in the tubular swirling chamber is generated. By such a defined swirling of the fluid, a proper mixing ratio of the air/fuel mixture and a stable flame on a pilot body surface in the tubular swirling chamber may be provided.
For injecting fluid radially, radial swirlers are attached to a pre-chamber of the tubular swirling chamber in order to generate a strong turbulence flow of the fluid in the pre-chamber. In conventional radial swirlers, the fluid is in general injected tangentially to an inner surface of the pre-chamber, so that a high tangential moment inside the pre-chamber and a vortex of the fluid inside the pre-chamber and a combustion chamber of the tubular swirling chamber may be generated. The vortex provides a turbulent swirling region in the vicinity of the inner lateral area and a slow, inturbulent flow in the core of the vortex.
The fluid flow inside the pre-chamber and the combustion chamber will be described in the following in more detail. Usually, the pre-chamber and the combustion chamber are formed tubular, wherein the diameter of the pre-chamber is smaller than the diameter of the combustion chamber. When the injected fluid flows from the pre-chamber to the combustion chamber of the tubular swirling chamber, the diameter and thus the available volume increases abruptly. Thus, an axial pressure drop occurs. Under the influence of the axial pressure drop, that is generated by the change in a diameter difference of the pre-chamber and the combustion chamber, the fluid flows in a longitudinal direction from the pre-chamber to the combustion chamber. In the region where the axial pressure drop occurs, the fluid expands abruptly which causes the fluid to turn from the lateral area inwards towards the centre axis of the pre-chamber and/or the combustion chamber. Then, the fluid flows in the vicinity of the centre axis in an axial counter-direction towards the swirler and towards a base area (pilot body surface) of the pre-chamber again. The region of the counter-direction flow may be called internal re-circulation zone. The internal re-circulation zone is located along the centre axis of the combustion chamber inside of the vortex. At the base area (pilot body surface) the air/fuel mixture may be ignited and forms a flame. Next, the ignited air/fuel mixture turns outwards in the direction to the lateral surface of the pre-chamber and meets the incoming fluid injected by the swirler. At the location, where the internal re-circulating flow meets the incoming flow from the swirler passages, a region of turbulence is generated. Between this region and the centre region a shear layer is formed, wherein an ignited air/fuel mixture on the one side of the shear layer and the injected fluid from the swirler on the other side of the shear layer flows again in the axial direction of the pre-chamber and the main chamber. In this manner a so-called “internal recirculation vortex core flow” inside the pre-chamber and the combustion chamber is generated. Hence, the benefit may be that in the vicinity of the pilot body surface (ignition area of the air/fuel mixture) a proper mixing ration of the air/fuel mixture, a slower velocity of the air/fuel mixture and thus a larger exposure time in the area of ignition may be provided, so that a more effective combustion may be achieved.
EP 0 957 311 A2 discloses a gas-turbine engine combustion. A lean burn combustor of a gas-turbine engine comprises a radial inflow pre-mixing and a pre-swirling burner with a central burner phase that forms an upstream wall of a pre-chamber of the combustor. A circular recess is formed in the burner phase, wherein the recess comprises at least one pilot fuel injector for introducing pilot fuel tangentially into the recess.
WO 2007/060216 A1 discloses a combustion apparatus in which combustion of a fuel/oxidant mix takes place. A pre-chamber is located to the combustion chamber and swirlers for supplying a gas to the pre-chamber are provided, so as to form a film of gas on the interior surface of the pre-chamber and thus prevent a combustion flame from the combustion chamber attaching itself to this interior surface damaging the pre-chamber. The film is provided by setting back a wedged piece of a swirler from a radially inner edge of an annular plate, so that an annular ledge on the annular base plate may be provided.
U.S. Pat. No. 6,253,555 B1 and U.S. Pat. No. 5,319,935 disclose a combustion chamber comprising mixing ducts with fuel injectors varying in number and cross-sectional area. First and second swirlers are arranged such that a fuel to air ratio of the fuel and air is swirled in opposite direction.